In the field, an obstacle normally refers to a three-dimensional object above the ground.
Nowadays, a common monocular-based obstacle detection method is based on motion compensation. The idea is that, when the road is flat and the lightning condition is fixed for a limited amount of time, for any of the points in the road plane, the pixel value of its image remains unchanged in consecutive frames. Assuming that each of the pixels of a previous frame corresponds to a point in the road plane, a hypothetical frame when the camera is moved is derivable, which can be calculated from the pixels of the previous frame according to camera motion parameters and imaging basics. Hence, the differences between the hypothetical frame and an actual one that is captured at the time are the sole result of those points that are not in the road plane. Pixels corresponding to the differences may be an obstacle above the ground.
The present method determines whether an obstacle is somewhere in an image based solely on the result from motion compensation. However, when the precision of motion parameters is low, or affected by image noise, the result from motion compensation may not be good, leading to something mistakenly detected as an obstacle.